The present invention relates to x-ray imaging systems, and in particular, to automated x-ray imaging systems capable of providing selectively enhanced volumetric image resolutions, e.g., for magnifying the field of view and providing a volumetric display image having features not otherwise visible to an unaided human eye.
Medical x-ray imaging has been and continues to be a very important tool for medical diagnostics. Such systems typically use x-ray film or digital electronic image sensors to record the intensity of the photons that pass through the subject. Conventional automatic exposure systems are often used to control the x-ray exposure by controlling things such as the voltage or current driving the x-ray source or controlling the exposure time to achieve the best exposure to the entire volume of the subject being imaged. Such systems use a signal acquired at the exit side of the subject of the x-ray imaging to control the exposure. In those systems using film, detectors, placed either in front of or behind the film, generate one or more signals based on the amount of x-ray exposure received. These detectors, calibrated to the film being used, provide signals which can be processed to determine and control the overall exposure. In those systems using electronic image sensors, the image signals provided by the sensor array can be used directly for monitoring the exposure and providing appropriate control signals.
Following completion of the x-ray imaging itself, the image in its film or electronic form is then typically checked for image quality by the attending technician. Later, that same film or electronic image is checked by a specialist, e.g., a radiologist, and a diagnosis is performed. Depending upon the results of the diagnosis, the subject may be brought back for additional x-ray imaging of the region or regions found to be of greater interest following the diagnosis. Such subsequent imaging will typically be performed with the collimator adjusted to focus on the specific regions of interest, and increased x-ray doses will be applied.
Images generated using x-ray radiation are often degraded by scattering of the radiation, low signal-to-noise ratio (caused by a desire for exposing the subject to as minimum a radiation dose as possible), requirements for large dynamic range, and saturation of the sensors used in the detector array (caused by x-ray radiation striking the imager without attenuation). While these problems can be minimized by the attending technician using collimators to isolate a region of interest, such technician is generally not qualified to read the images or determine the appropriate areas of interest. Further, during many procedures, the patient is under some discomfort during the procedure and is, therefore, removed from the imaging system prior to any reading of the film or image. Accordingly, significant percentages of subjects are recalled for additional imaging.
These types of problems become increasingly significant as the sizes and scales of the features sought to be viewed decrease. For example, a number of studies have revealed the role of angiogenesis, i.e., the formation and differentiation of blood vessels, in the development of cancer and other diseases. Corresponding trials with antiangiogenic approaches to treatment have been used with some success. Accordingly, techniques for evaluating tissue vascularization have become increasingly important. The well-known technique of computed tomography (CT) and magnetic resonance imaging (MRI) have been used most frequently to evaluate tumor malignancy and the effects of various therapies on the patients. Typically, contrast enhancement materials are used for purposes of improving the resulting images. However, accurate imaging of the blood vessels present has relied primarily upon estimations based on the accumulation of the contrast medium within the small spaces among the vessels, generally as a result of increased vessel leakage. Further, the small sizes of the blood vessels within the tumors are difficult to assess with typical scanner equipment due to low sensitivity of the contrast media and low signal-to-noise ratio (SNR) when using high local resolution scanning. These problems can often be overcome by using micro-CT (e.g., using a synchrotron source providing an intense collimated beam of monochromatic x-rays) or volumetric CT (e.g., using multiple flat panel detectors or multiple rows of detectors to scan a volume of the subject). However, the problems discussed above concerning real-time evaluation and focusing upon the region of interest remain.
Accordingly, it would be desirable to have an x-ray imaging system capable of determining, focusing upon and selectively increasing, in a real time manner, the volumetric image resolution of the regions of the subject being of the most interest.